In conventional combustion chambers, the chamber wall is made of metal, and the support of the plug-guide is likewise made of a metal that is compatible with the metal of the chamber wall. The base of the support is welded to the outside face of the chamber wall around the opening.
With the increases in the temperature that exists within combustion chambers, where such increases in temperature are needed to improve the performance of aviation engines, it is no longer feasible to use chamber walls made of metal. This means that it is impossible for the plug-guide support to be welded to the chamber wall. This applies in particular when the chamber wall is made of a composite material comprising carbon fibers embedded in a ceramic matrix.
In its FIG. 2, U.S. Pat. No. 6,351,949 shows a combustion chamber of the type specified in the introduction above, in which the base of the support of the plug-guide appears to be fixed to the outside face of the chamber wall by welding around the opening. That document also shows removable means for introducing air into the combustion chamber, said means comprising a cylindrical sleeve passing through an orifice of the chamber wall and presenting a collar bearing against the inside face of the chamber wall, together with means for mechanically securing said sleeve disposed on the outside face of the chamber wall. The sleeve is made of a metal material that withstands high temperatures, and preferably of a ceramic material. That document does not suggest that the plug-guide could include a collar at its radially-inner end for fixing in the same manner against the chamber wall. Furthermore, it would be impossible to mount such a modified support since the plug-guide is held by an end portion of the support which is of a diameter greater than that of the base of said support, and the diameter of the opening is smaller than that of the collar and than that of the end portion.